Many popular wavetable synthesizers are astonishingly bad at suppressing artifacts - even on a high-quality setting some create artifacts as high as -36 dB to -60 dB (level difference between fundamental on artifacts) which is well audible, and furthermore often dampening the highest wanted audible frequencies in the process, to try and suppress this unwanted sound.
Artifacts mean that you are (perhaps unknowingly) crowding your mix with unwanted tones / frequencies. Without considerable care and a whole lot of number crunching, this process will create audible artifacts. Playback of wavetables requires digital resampling to play different frequencies.
